Distinguishable electron method (DEM) for electronic structure calculations. V. Static polarizability of H2 in the screened valence bond (Wang) approximation

The distinguishable electron method is used to calculate the static polarizability tensor of H2, at three different internuclear distances, starting with the screened valence bond (Wang) initial approximation. As usual, a first-order correlation correction is obtained by means of accessible expressions which do not require correlated wavefunctions. Since the polarization potential is linear in the Cartesian electron coordinates, the one-electron molecular perturbation functions can be determined exactly from pure atomic equations. Our results are comparable to the coupled Hartree-Fock values, but are obtained much more easily. Finally, it is shown that nonsymmetric perturbation treatments, which ignore exchange, are unsatisfactory because of large errors in determining the first-order correlation correction.